The Japan Mint instituted the 'Sundays' series of badges in 1948. Actually, according to the histories of the Mint that I have read, the first badge was created as a trial of some sorts and only available in small quantities. They proved to be a popular item, so the Mint has been making them every year. The first three (1948, 1949, 1950) medals are larger table medals, but from 1951 the medals became badges. These badges had no ribbon and are complete as shown below. The earlier medals and badges are not often encountered, but since they were popular, they are probably still gathering dust on shelves across Japan.

I have seen a few larger medals as well as badges of some of these, so it may be possible that both were minted for each year.

Most show the national holidays of Japan, too, and the animals represent the creatures in the Chinese zodiac.

1954

1955

1959

1958

1960Note the Mitsubishi emblem on the top rat. The 1960 badge to the right doesn't have the same emblem, so this was probably specially made for Mitsubishi employees, or perhaps it was a paid advertisement. See the badge below

'The Sundays of 1948'

1960

1952

1966

1968

1970

1971

1972

1974

1975

1978

1979

1962

1965

1973

1974--large medal

1960 badge. Note that on the 2 examples above, the 'Made at the Japan Mint' stamp is on the reverse under the banners. On this badge a company name is in its place (Itoman) and the Mint stamp is on the obverse under the mice.As stated above, this may have been a paid ad or minted expressly for Itoman employees.